Curve from Mesh, how to enable handles?
Toggle Edit Mode and set Spline Type to Bezier. 



Tool Shelf T > Tools > Curve Tools > Set Spline Type:



Here is an explanation from the Blender Reference Manual:


  Mesh objects that consist of a series of connected vertices can be
  converted into curve objects. The resulting curve will be a Poly curve
  type, but can be converted to have smooth segments as described above.